I am working on a volunteer project and we are in desperate need of a baseline layer. I have been unable to find it anywhere (there are plenty of shoreline and coastline layers out there) does anyone have a source for this data?

Thanks, Dave
The baseline from which the territorial sea is measured is mainly the low-water line along the coast as marked on large-scale charts officially recognized by the coastal state.

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    Please describe to the GIS-SE users your definition of a 'baseline layer'
    – Mapperz
    Commented May 16, 2013 at 16:37
  • Confirm this please en.wikipedia.org/wiki/Shifting_baseline
    – Mapperz
    Commented May 16, 2013 at 16:38
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    this is the best definition i have found wiki.openstreetmap.org/wiki/Tag:boundary%3Dmaritime Commented May 16, 2013 at 17:14
  • I do see a problem with the word "mainly". Is it mainly low water unles it is high water? Is there some other deliniation. How do you map from one and switch to another? if it is the shifting baseline above what does it shift to and when (at coastal state lines)?
    – Brad Nesom
    Commented May 16, 2013 at 18:44

1 Answer 1


The actual territorial sea boundary is maintained by NOAA and distributed here: http://www.nauticalcharts.noaa.gov/csdl/mbound.htm

You may need to contact the Chief Geographer for NOAA to see if the current baseline is available in a format you need; as I didn't find a nice packaged link either.

I was working in this area a number of years ago, and would like to point out that in a number of states, the baseline used for calculating the maritime boundaries has been fixed. In those cases, the baseline points are probably available in the Code of Federal Regulations. Otherwise, the baseline is ambulatory as new rocks or subsiding shorelines are identified.

Edit: I think the fixed baseline may only be relevant to mineral leasing (e.g. BOEMRE) , and not territorial seas.

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